"Sebastian!"

Jace knew his foster brother rather hated that name - a pseudonym, an alias, a stolen name from a murdered child. Jace, frankly, didn't care. However, as time wore on, he found himself refering to Lilith's son as 'Jonathon', the name they had shared for seventeen years. (Jace knew that Clary was the only one who called her brother Jonathon, while Isabelle and Alec called him Sebastian, refusing to admit a connection between their brother and their brother's killer.) But when Jace called him Sebastian, they both know he was angry.

And Jace was ballistic.

He was furious with his brother, who was Clary's brother (did he not care they were related, that she was taken, perfectly happy?) Maybe Clary was right and he was only a demon, with nothing in that black heart of his. But Jace knew Sebastian's heart. Jace's heart was Sebastian's heart; the proof of that was painted on his chest in the shape of a child's hand.

Maybe Sebastian just wanted his heart back. If he could, Jace would have gladly given it to him, but Sebastian's heart was Jace's heart, and he had given it to Clary.

"Sebastian, you motherf***er, get down here!"

"I do believe you mean sister f***er. Of course, it didn't get quite that far, I can assure you." Jace whirled around to see Sebastian standing on one of the rafters. Jace saw red for a minute, and then he was lunging at the demon-boy, all ready to choke the life out of him, to see the light dim in his lecherous eyes. Jace wanted to stab him through the spine again. He wanted to dismember him, castrate him, gouge his eyes out, take off his other hand, along with the arms.

But Sebastian had the same gifts Jace did, and so they entered into a deadly dance, a murderous game of wiles and wounds. Sebastian was sure he would win, for though Jace's skills matched his, Sebastian still had a clear head - and that would make all the difference.

"Did she cry when she told you?" Sebastian mocked. "Or was she angry? I bet she was ashamed - why else wait so long before telling you?" Jace couldn't respond, just howled in rage as he pounced on his foster brother, dodging a blade, blocking a fist. The older boy's words were more infuriating in part because they were also true. Clary had cried when she told him, she had been ashamed. There was no anger, just a crushing sadness; he had been furious enough for the both of them.

He smiled at her, and she smiled tenatively back. He traced her lips with his finger, and she gasped. Slowly, he put his hands on each side of her head and brought her face to his.

Jace grunted as Sebastian's knee hit him in the gut. Before going out he had insisted Alec put a Numb rune on him, which would dull a little of the pain he knew would come with a fight with his brother. It wasn't like Clary's Fearless rune (what was?) but it was the best his parabatai could do. Alec had tried to insist on coming, but Jace wouldn't hear of it - partly because Alec still didn't know about Jonathon/Sebastian. But that was just it - the matter was private, just for the three of them: Jace, Clary, and Sebastian.

Jace lashed out and caught Sebastian on the cheek with his nails. The demon-boy pulled back, surprised at such a dishonorable hit. But Jace wasn't fighting for his honor. He was fighting for Clary's.

"Stop!" she cried. He froze, his lips inches away from hers. What was wrong? What had he done? His alarm grew as he saw tears gather in her eyes.

"Jace...Jace I'm sorry, I'm just-"

"Clary, what's wrong? What am I doing? You've been like this for a while - if I hurt you, or insulted you, you need to tell me-"

"Oh, no, not you, Jace! Not you," she exclaimed, eyes going wide. She looked lost, hurt. As if she didn't know who to turn to. "It's just - it's just...he...he..." and the tears ran down her cheeks.

"I'm going to kill you," Jace growled. Their fight was going nowhere; it was a stalemate. Jace wanted to knock that sinister smile off those unholy lips but he knew his words were almost akin to an empty threat.

An angry, alarmed buzzing sounded in his head.

"I'm not going anywhere you aren't," Sebastian answered as he pivoted out of the way. "Do you know I watched you? That night at the club, when you two danced the night away?" Jace growled and started throwing punches, not caring where they landed as long as it was on him. Jace's eyes widened as Sebastian's voice sounded right near his ear,

"She belongs to both of us, you know. You two are a perfect match, but she's still mine. She and I are the very last of the Morgensterns - she is the only one who shares the same blood as me. Every. Single. Drop."

"Not every drop," Jace hissed as he spun around.

"He's a demon - I've told you over and over Jace. A demon; he has no heart," Clary whispered. She shook her head but did not resist him when he gathered her in his arms. He pressed his lips against her hair.

"What happened, Clary? Please, please, please tell me. Maybe I can help."

"You're too late - it's already done."

"Mmm, that's true, isn't it? She has angel blood whereas I'm full of evil." Sebastian laughed, then winced as Jace's blade (Raphael) sliced his arm. He growled and lunged, ripping at Jace's shoulder in retaliation. "Did she ever tell you that's not the first time our lips were together? Did you know we've kissed before - with mutual consent, that I can promise you."

She sobbed out her story, and Jace's heart constricted. How dare he! I'm going to kill him! and I'll make him regret everything he's ever done, was his train of thought.

The buzzing became a roar.

"You're lying," Jace said. Sebastian shrugged and they were silent as they continued their battle. They were even matched, and their fight dragged on. At some point, Sebastian was pushing Jace back into a wall, and then somehow Jace got the upper hand. Wrestling with Sebastian, Jace threw him on the ground and held him down with his foot. Jace raised his seraph blade -

"Kill me and you kill yourself," Sebastian hissed at him. Jace wondered why he didn't try to move the other's foot - perhaps he was giving up? Or maybe he knew what Jace knew, that Sebastian was right, that this fight was destined to have no winner.

"I've died before," Jace replyed coldly, adopting an indifferent expression. Sebastian chuckled, seeing through the facade.

"Yeah, and so have I. But Clary hasn't. And if you die -" Sebastian leaned up a bit to emphasize his next point - "she might as well. You think she can survive without you? She's strong, and she might recover - but do you want to give her a reason to have to?"

Jace couldn't come up with an answer. He realized he had never hated his brother as much as now, because he knew he was right. The most he could was rough Sebastian up, make him bleed but in the end Jace would always come back, and when their wounds healed, Sebastian would turn back into Jonathon, and Clary would always be in the middle. Like her brother said, she belonged to both of them, and neither was going to give her up.

Jonathon was right.

And Jace cursed him for it.

A.N-Finally, Valentine's Brood is finished! This wasn't how I pictured it going when I wrote the first chapter, but then ideas started forming for another one-shot, and so I decided to combine them. Now, about the mess with Clary and Sebastian/Jonathon: I know all Sebastian did was kiss her, but I think that idea that Sebastian would do that, and hold her down, combined with the brother/sister factor, just freaked Clary out too much, and that's why she kind of broke down a little.

I'm not good at fight scenes, and I knew I couldn't have one of them die - that just isn't real. So I was racking my brain for a way to end this chapter, and I hope I ended it on a good note. Throughout this whole story, I tried to make the characters' thinking sporadic, with short bursts of flow. I wanted it messy, but clean enough that it sill seemed like poetry. I also tried to incorporate quotes or teasers from the TMI and TID series into this, because I think it makes it more special